1. Field of the Invention
The present invention relates to a circuit for generating a start pulse signal for a source driver integrated circuit (IC) in a thin film transistor-liquid crystal display (TFT-LCD) and in particular to an improved circuit for generating a start pulse signal for a source driver IC in a TFT-LCD which can remarkably reduce a layout area, and restrict setup and hold violations.
2. Description of the Background Art
In general, a TFT-LCD that is a kind of an active LCD is thin and light-weighted and consumes small power, and thus has been popularly used for a portable display device, such as a notebook computer. Nowadays, the TFT-LCD is even employed for the operation of vehicles and the audio/video of monitors.
A start pulse signal STH is a control signal inputted to a source driver IC through a timing controller in the AFT-LCD. The start pulse signal STH serves to inform that an effective input data is included in data inputted from a data driver to the source driver IC. A circuit for generating the start pulse signal STH generates the start pulse signal STH at an initial period of a data enable signal DE. The constitution and operation of a conventional circuit for generating the start pulse signal will now be described with reference to FIG. 1.
FIG. 1 is a circuit diagram illustrating the conventional circuit for generating the start pulse signal, including: a 5 bit counting unit 10 for counting a main clock signal MCLK; an AND gate AND1 for receiving a data enable signal DE and a reset signal Reset; a latch unit 20 consisting of first to fifth flip-flops 21xcx9c25 for respectively receiving the output signal from the 5 bit counting unit 10 as an input signal S, the main clock signal MCLK as a trigger input, and the output signal from the AND gate AND1 as a reset signal R, and feedback-inputting an output signal D to the 5 bit counting unit 10; a decoding unit 30 consisting of a NAND gate NA1 for receiving a complementary signal of the output signal D from the first to fourth flip-flops 21xcx9c24, and an AND gate AND2 for receiving complementary signals of output signals from the NAND gate NA1 and the fifth flip-flop 25; and a sixth flip-flop 40 for receiving the output signal from the NAND gate NA1 and a complementary signal of the output signal from the AND gate AND2 as input signals S, Sxe2x80x2, the reset signal Reset as a reset signal R, and the main clock signal MCLK as a trigger input T, and generating the start pulse signal STH.
When the reset signal Reset and the data enable signal DE are at a high level, the first to fifth flip-flops 21xcx9c25 of the latch unit 20 receive the main clock signal MCLK as the trigger input T and convert output signals in a clock leading edge. Here, the output signals D from the first to fifth flip-flops 21xcx9c25 are inputted to the decoding unit 30, and at the same time feedback-inputted to the 5 bit counting unit 10.
The decoding unit 30 combines the output signals from the first to fifth flip-flops 21xcx9c25, and inputs it to the sixth flip-flop 40 for generating the start pulse signal STH.
The sixth flip-flop 40 receives the output signal from the NAND gate NA1 and the complementary signal of the output signal from the AND gate AND2 as input signals S and Sxe2x80x2, the reset signal Reset as a reset signal R, and the main clock signal MCLK as a trigger input T, thereby generating the start pulse signal STH.
However, as illustrated in FIG. 1, the conventional circuit for generating the start pulse signal includes the 5 bit counting unit 10 for receiving and counting the main clock signal MCLK, the latch unit 20 consisting of 5 flip-flops for latching the output from the counting unit 10, the decoding unit 30 for decoding the output signal from the latch unit 20, and the flip-flop for generating the start pulse signal by synchronizing the output signal from the decoding unit 30 to the main clock signal MCLK. As described above, the conventional circuit for generating the start pulse signal requires many devices, which results in increase of a chip area. In addition, the setup and hold violations are generated.
Accordingly, an object of the present invention is to provide a circuit for generating a start pulse signal for a source driver IC in a TFT-LCD which can remarkably reduce a layout area and restrict setup and hold violations, by generating the start pulse signal by a simple circuit for detecting a leading edge of a data enable signal, instead of a complicated counter circuit.
In order to achieve the above-described object of the present invention, there is provided a circuit for generating a start pulse signal for a source driver IC in a TFT-LCD, including: a first latch unit for receiving a data enable signal and a reset signal, extracting a leading edge of the data enable signal in a leading edge of a main clock signal, and latching the data enable signal in a trailing edge thereof; a logic gate unit for receiving a complementary signal of the output signal from the first latch unit and the data enable signal, and generating a pulse signal in a leading edge of the data enable signal; and a second latch unit for receiving the output signal from the logic gate unit and the reset signal, outputting the output signal from the logic gate unit as a start pulse signal in the leading edge of the main clock signal, and latching the output signal from the logic gate unit in the trailing edge thereof.
In accordance with a preferred aspect of the present invention, the first latch unit is an RS flip-flop.
In accordance with another preferred aspect of the present invention, the logic gate unit is an AND gate.
In accordance with still another preferred aspect of the present invention, the second latch unit is a D flip-flop.